annotate en/concepts.tex @ 108:e0b961975c5e
First bit of concepts chapter.
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Bryan O'Sullivan <bos@serpentine.com> |
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Thu Nov 09 10:11:31 2006 -0800 (2006-11-09) |
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1 \chapter{Behind the scenes}
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2 \label{chap:concepts}
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3
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4 Unlike many revision control systems, the concepts upon which
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5 Mercurial is built are simple enough that it's easy to understand how
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6 the software really works. Knowing this certainly isn't necessary,
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7 but I find it useful to have a ``mental model'' of what's going on.
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8
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9 \section{Tracking the history of a single file}
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10
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11 When Mercurial tracks modifications to a file, it stores the history
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12 of that file in a metadata object called a \emph{filelog}. Each entry
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13 in the filelog contains enough information to reconstruct one revision
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14 of the file that is being tracked. Filelogs are stored as files in
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15 the \sdirname{.hg/data} directory. A filelog contains two kinds of
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16 information: revision data, and an index to help Mercurial to find a
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17 revision efficiently.
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18
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19 For small files without much history, the revision data and index are
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20 combined in a single file (with a ``\texttt{.i}'' suffix). A file
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21 that is large, or has a lot of history, has its filelog stored as
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22 separate data (``\texttt{.d}'' suffix) and index (``\texttt{.i}''
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23 suffix) files. The correspondence between a file in the working
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24 directory and the filelog that tracks its history in the repository is
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25 illustrated in figure~\ref{fig:concepts:filelog}.
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26
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27 \begin{figure}[ht]
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28 \centering
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29 \grafix{filelog}
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30 \caption{Relationships between files in working directory and
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31 filelogs in repository}
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32 \label{fig:concepts:filelog}
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33 \end{figure}
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34
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35 %%% Local Variables:
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36 %%% mode: latex
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37 %%% TeX-master: "00book"
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38 %%% End:
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